Senate Majority Leader Harry Reid is refusing to let go of his allegation that Mitt Romney paid no taxes for 10 years, despite repeated denials by the GOP nominee.

In a statement Thursday night responding to criticism, Reid said he was told by an "extremely credible source" Romney didn't pay taxes for a decade, and that the nominee is "hiding something" by refusing to release more tax returns.

Here's Reid's full statement:

"There is a controversy because the Republican presidential nominee, Governor Mitt Romney, refuses to release his tax returns. As I said before, I was told by an extremely credible source that Romney has not paid taxes for ten years. People who make as much money as Mitt Romney have many tricks at their disposal to avoid paying taxes. We already know that Romney has exploited many of these loopholes, stashing his money in secret, overseas accounts in places like Switzerland and the Cayman Islands.

“Last weekend, Governor Romney promised that he would check his tax returns and let the American people know whether he ever paid a rate lower than 13.9 percent. One day later, his campaign raced to say he had no intention of putting out any further information.

“When it comes to answering the legitimate questions the American people have about whether he avoided paying his fair share in taxes or why he opened a Swiss bank account, Romney has shut up. But as a presidential candidate, it’s his obligation to put up, and release several years’ worth of tax returns just like nominees of both parties have done for decades.

“It’s clear Romney is hiding something, and the American people deserve to know what it is. Whatever Romney’s hiding probably speaks volumes about how he would approach issues that directly impact middle-class families, like tax reform and the economy. When you are running for president, you should be an open book.

“I understand Romney is concerned that many people, Democrats and Republicans, have been calling on him to release his tax returns. He has so far refused. There is only one thing he can do to clear this up, and that’s release his tax returns.”